I used to think that I would be surfing the web or doing stuff with the phone in the horizontal (or if you will have it, landscape) orientation. However, once I got my very first smartphone, I had been using it vertically almost 99% of the time.
I seldom use my iPad horizontally either (for web surfing) so I was amused that I've never given much thought to this behaviour until I came across the Mashable article just now. I'm not surprised that the web is getting better in the vertical format because tablets and smartphones are taking over from desktops and laptops. Besides, monitors are getting larger and higher resolution at pretty affordable prices these days.
I don't think I'll be changing the orientation of my desktop monitor (not that I have much of a desktop considering the USB ports no longer work and its CPU is a very slow single core Pentium 4) to portrait anytime soon but who knows? How do you read your stuff on your smartphone or tablet? Will you be turning your LCD monitors by 90 degrees?